Temperature%20Regulation

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Temperature Regulation

• Dr Dileep
  Verma
• Associate Professor
• Deptt of Physiology
• KGMU

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Lecture-1 Topics

• Core and Shell body temp.
• Heat Balance
• Factors promoting -
• a) Heat gain
• b) Heat loss
• Temp. regulatory mechanisms

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Learning Objectives

• Normal Body Temperature
• Ways of measuring Body Temp
• List the mechanisms of heat production heat
  loss
• Regulation of Body Temp.

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Body Temperature

• Normal Body Temperature (NBT)
• 98.60F(370C)
• Range of NBT ----- (970F to 990F)
• Rectal Temp ----- (0.50F to 10F) above
  the Oral
• Rectal Temp reflects the internal body Temp
  (Core Body Temp)
• Core Body Temp remain almost constant
• Skin Temp (Shell Temp)-----Variable

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Temperature Homeostasis

• Keep the body temp within a very narrow range
• Range of NBT (970F to 990F)
• Temperatures above this
• denature enzymes and block metabolic pathways
• Temperatures below this
• slow down metabolism and affect the brain.

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Heat Balance

• Heat balance maintains the body temp
• Balance between heat production heat loss (Heat
  Balance)
• Heat Balance
• Heat production Heat loss
• Heat production is called thermogenesis
• Heat loss is called as thermolysis

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Heat Production (Thermogenesis)

• BMR
• Specific Dynamic Action of food
• Activity of skeletal muscle
• Shivering
• Exercise
• Chemical Thermogenesis
• Epinephrine Norepinephrine
• Thyroxine
• Brown Fat-
• Source of considerable heat production
• Abundant in infants

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Heat Loss (Thermolysis)

• Radiation
• Conduction
• Convection
• Evaporation
• Perspiration
• Respiration
• Loss through urine feces

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Role of Skin
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Heat Exchange in the Skin
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Vasoconstriction and Vasodilatation
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Thermoregulation

• Temperature is regulated by nervous feedback
  mechanisms
• Thermoregulatory center located in the
  Hypothalamus
• Thermoregulatory regulatory responses include
• Autonomic
• Somatic
• Endocrine
• Behavioural changes

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Feedback system

• 1) Receptor
• Sensor that responds to changes (stimuli)
• 2) Control Center
• Sets range of values
• Evaluates input and
• Sends output
• 3) Effector-
• Receives output from control centre
• Produces a response

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Body Temperature Control System

• Hypothalamus
• Acts as a thermostat
• Receives nerve impulses from cutaneous
  thermoreceptors
• Thermoreceptors Cold Heat
• Hypothalamus- also has thermoreceptors called
  central thermoreceptors
• These detect changes in blood temperature

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Thermoregulatory regulatory responses

• Activated by Exposure to Cold
• Shivering
• Increase voluntary activity
• Increase TSH secretion
• Increase Catecholamines
• Vasoconstriction
• Horripilation
• Curling up

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Thermoregulatory regulatory responses

• Activated by Exposure to Heat
• Vasodilatation
• Sweating
• Increase in Respiration
• Anorexia
• Apathy
• Decrease TSH secretion

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Thermoregulatory regulatory responses

• Exposure to Cold
• Shivering
• Increase voluntary activity
• Increase TSH secretion
• Increase Catecholamines
• Vasoconstriction
• Horripilation
• Curling up

• Exposure to Heat
• Vasodilatation
• Sweating
• Increase in Respiration
• Anorexia
• Apathy
• Decrease TSH secretion

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1-A major source of heat production in infants is

1. Increased muscular activity
2. Brown fat
3. Increased sympathetic activity
4. Specific dynamic action of food

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2-At normal room temperature most body heat loss
is by-

1. Convention
2. Conduction
3. Radiation
4. Sweating

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3-Constituents of secreted sweat are similar to
plasma except for

1. Proteins
2. Chloride
3. Bicarbonate
4. Potassium

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4-The only available mechanism of heat transfer
when the environmental temperature is greater
than the body temperature is

1. Radiation
2. Conduction
3. Convection
4. Evaporation

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5-Cause of thermogenesis in the body is

• Skeletal muscle relaxation
• Assimilation of food
• Decreased cardiac metabolism
• Hypothyroidism

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6-A major factor resulting in increase in body
temperature during exercise is-

• Heat dissipating mechanisms inefficient
• Enormous thermogenesis
• Vasoconstriction on non-working muscles
• Resetting of thermostat

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7-Site which reflects the true value of core
temperature

• Oesophagus and rectum
• Tympanic membrane
• Vagina
• All of the above

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8-BMR is dependent on

• Body weight
• Surface area
• Amount of lean body mass
• Height

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9-One feels hotter on a humid day because-

• Rate of sweating increases
• Surrounding temperature is more
• Heat loss by the body via process of radiation
  decreases
• Rate of evaporation of water from body decreases

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10-A major factor resulting in increase in body
temperature during exercise is-

• Heat dissipating mechanisms inefficient
• Enormous thermogenesis
• Vasoconstriction on non-working muscles
• Resetting of thermostat

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Temperature Regulation

• Dr Dileep
  Verma
• Associate Professor
• Deptt of Physiology
• KGMU

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Lecture-2 Topics

• Life in Hot environment
• -Effect of acute heat
• Thermoregulatory responses
• Heat syndrome
• -Heat cramps
• -Heat exhaustion
• -Heat stroke

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Contd

• Life in cold environment
• -effect of acute long term
• cold exposure on body
• Applied
• -Hypothermia
• -Harmful effects of extreme
• cold

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Learning Objectives

• Effect of Hot Cold environment on the body.
• Thermo-receptors
• Regulation of Body Temperature

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Life in Hot environment

• Hot climates- These are two types
• a) Hot-dry
• b) Warm-humid
• Hot-dry climate-
• Found in deserts
• Temp gt500 C
• Not humid
• Warm-humid climate
• Found in tropical forest
• Temp usuallylt350 C
• Humidity gt75

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Contd----

• Effects of acute heat -
• Effects of acute exposure to heat are divided
  into-
• a) Thermoregulatory responses
• b) Other effects

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Contd----

• Thermoregulatory regulatory responses

Vasodilatation Sweating Increase in
Respiration Anorexia Apathy Decrease TSH secretion
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Contd----

• Other effects of acute heat exposure on-
• Cellular metabolism
• Rate of respiration
• Work of breathing
• Pulse rate
• Dehydration
• Urinary volume

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Contd----

• Heat Syndromes- adverse reaction to heat
  exposure
• a) Heat Cramps
• b) Heat Exhaustion
• c) Heat Stoke

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Life in cold environment

• Effect of cold exposure on body-
• a) Acute cold exposure
• b) Long term cold exposure
• Applied
• -Hypothermia
• -Harmful effects of extreme
• cold

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Contd----

• Effect of acute cold exposure on body

Shivering Increase voluntary activity Increase
TSH secretion Increase Catecholamines Vasoconstric
tion Horripilation Curling up
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Contd----

• Effect of long term cold exposure
• Metabolic Responses
• Insulative Responses
• Hypothermic Responses

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Contd----

• Hypothermia Body temp below the normal lower
  limit (lt970F)
• Thermoregulatory responses
• Greatly impaired at (lt940F)
• Lost at body temp(lt850F)

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Contd----

• Frostbite
• Occurs at very low temp
• Surface area freezes
• Ice crystals formed
• Common sites-
• Lobes of the ears
• Digits of hands
• Digits of feet
• Cold induced vasodilatation-
• Final protection against
  frostbite

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Summary of Effector Mechanisms in Temperature
Regulation
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1- Thermal sweating differs from non-thermal
sweating in that

• Eccrine glands are responsible for it
• Occurs due to activation of sympathetic
  cholinergic nerves
• Found mainly over palm, sole and axilla
• All of the above

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Core temperature of 260C leads to death due to

• Brain damage
• Respiratory insufficiency
• Cardiac failure
• All of the above

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2- Which area of hypothalamus functions as
thermostat?

• Preoptic
• Paraventricular
• Dorso medial
• Lateral

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3- Insensible water loss (perspiration) will be
absent if humidity is

• 50
• 70
• 90
• 100

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4- Pyrogens raises body temperature by

• Setting the thermostat to higher level
• Releasing interleukins
• Decreasing peripheral heat liberating mechanism
• Causing peripheral vasoconstriction

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5- Heat loss process of the body not directly
under physiological control is

1. Radiation from body
2. Conduction and convection to surroundings
3. Vaporization of sweat
4. Warming of inspired air

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6- Fever is usually caused by

• Interleukin-1
• Substance- p
• Endorphins
• Encephalin

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7- During exposure to cold, body temperature is
raised by

• Vasoconstriction in the skin
• Horripilation
• Thermogenesis
• All of the above

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8- Profound hypothermic signs include all except

1. Show breathing
2. Bradycardia
3. Hypotension
4. Hyperactivity

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9- Aspirin decreases the body temperature by

• Inhibiting interleukin-1
• Inhibiting pyrogens release
• Killing fever producing organisms
• Inhibiting prostaglandin synthesis

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10- When the core temperature of the body falls
below the hypothalamic set-point temperature

• The blood vssels of the skin constrict
• Heat production increases within minutes
• The basal metabolic rate increases
• All of the above

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